Device for determining energization state of alternating-current electric arc furnace, method for operating alternating-current electric arc furnace, and alternating-current electric arc furnace

Abstract

Provided is a technique with which it is possible to quickly determine the energization state in an AC electric arc furnace and to stably determine the furnace condition without being affected by dust. This energization state determination device for an AC electric arc furnace is provided with: a detection means for detecting sound generated in the AC electric arc furnace; an output unit which analyzes the frequency of the detected sound and outputs a frequency-sound pressure signal; and a determination means for determining the coverage state of an arc caused by slag formation on the basis of the signal intensity in the range of Fi-0. 5 * F0 to Fi + 0.5 * F0, where Fi is a frequency that is an integral multiple of the fundamental frequency F0 of the AC electric arc furnace. A method for producing molten steel by melting and refining waste material in an AC electric arc furnace controls any one of the oxygen-containing gas supply rate, the carbon material supply amount, and the slag-making material input amount, or a combination of a plurality thereof, on the basis of the energization state determined by the device.

Description

Technical Field

[0001] The present invention relates to an apparatus for determining an energization state based on a sound generated inside an AC arc furnace, a method for operating an AC arc furnace using the apparatus, and an AC arc furnace equipped with the apparatus. Background Art

[0002] An arc furnace is a furnace that generates an arc between an electrode and a charge inside the furnace and performs heating and melting. Generally, the temperature of the arc exceeds 2000°C, so the heat loss due to radiation is large. In order to reduce the heat loss due to this radiation, it is known that it is effective to shield the arc light by forming slag. Therefore, in order to improve the energization efficiency, it is important to detect the slag formation situation inside the furnace. In addition, slag forming also has the effect of reducing the entrainment of the atmosphere into the molten steel, and can also suppress the nitrogen absorption reaction into the molten steel. Therefore, in order to produce high-quality molten steel, it is also important to maintain the slagging state.

[0003] Based on such a background, various slag formation detection techniques in an electric furnace have been studied so far. In the technique described in Patent Document 1, a method for detecting the slagging state during energization by monitoring the NOx concentration in the exhaust gas is disclosed. In addition, in the technique described in Patent Document 2, a method for directly monitoring the slag height inside the furnace by using microwaves is disclosed. In addition, in the technique described in Patent Document 3, a method for measuring the vibration and sound of the furnace body and indirectly estimating the slagging state is disclosed.

[0004] [Prior Art Documents]

[0005] [Patent Documents]

[0006] Patent Document 1: Japanese Patent Laid-Open No. 10-226812

[0007] Patent Document 2: Japanese Patent Laid-Open No. 07-166222

[0008] Patent Document 3: Japanese Patent Laid-Open No. 2013-170748 Summary of the Invention

[0009] [Problems to be Solved by the Invention]

[0010] However, in the prior art, there are the following problems.

[0011] In the method described in Patent Document 1, since the determination is made using the components in the exhaust gas, there is a time lag from the moment when the energization state inside the furnace changes to the detection of the exhaust gas components, and there is a problem that it is difficult to perform real-time slagging control.

[0012] In the method described in Patent Document 2, when the amount of dust generated in the furnace is large, noise is superimposed on the signal, so there is a problem that the slagging state cannot be stably detected.

[0013] In the method described in Patent Document 3, although it can be detected relatively quickly and is not easily affected by dust in the furnace, etc., in the frequency measurement below 500 Hz, the influence of the sound in the factory other than the arc sound is large, and there is a problem that stable furnace condition determination cannot be performed.

[0014] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a power-on state determination device for an AC arc furnace, an operation method for an AC arc furnace, and an AC arc furnace that can quickly determine the power-on state in the furnace and can stably determine the furnace condition without being affected by dust.

[0015] [Means for Solving the Problem]

[0016] The power-on state determination device for an AC arc furnace of the present invention that effectively solves the above problems is characterized by including: a detection unit that detects the sound generated in the furnace of the AC arc furnace; an output unit that analyzes the frequency of the detected sound and outputs a frequency-sound pressure signal; and a determination unit that, when setting the frequency that is an integer multiple of the fundamental frequency F0 of the AC arc furnace as Fi, determines the covering state of the arc caused by slagging based on the signal intensity in the range of Fi - 0.5×F0 to Fi + 0.5×F0.

[0017] It should be noted that in the power-on state determination device for an AC arc furnace of the present invention, the following (a) to (c) etc. can be more preferable solutions.

[0018] (a) When setting the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination unit determines based on the signal intensity of the center frequency in the range of Fi - 0.5×F0 to Fi + 0.5×F0.

[0019] (b) When setting the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination unit determines based on the intensity ratio of the signal intensity of one of the higher frequencies and the signal intensity of one of the lower frequencies in the range of Fi - 0.5×F0 to Fi + 0.5×F0.

[0020] (c) The difference between the two frequencies for obtaining the intensity ratio is 10 Hz or more and 40 Hz or less.

[0021] The method for operating an AC electric arc furnace according to the present invention, which effectively solves the above problems, is characterized in that when melting and refining scrap to produce molten steel in an AC electric arc furnace, based on the energization state determined by using any one of the above devices, any one of the supply rate of the oxygen-containing gas, the supply amount of the carbon material, and the input amount of the slag-making material is controlled, or a plurality of them are controlled in combination.

[0022] The AC electric arc furnace according to the present invention, which effectively solves the above problems, is characterized by including any one of the above devices.

[0023] [Effects of the Invention]

[0024] According to the energization state determination device, the operation method, and the AC electric arc furnace of the present invention, the energization condition inside the furnace can be quickly determined, and the furnace condition can be stably determined without being affected by dust. Therefore, the electric power unit consumption of the AC electric arc furnace can be reduced, which is industrially useful. Description of the Drawings

[0025] Figure 1 It is a graph comparing the change in the sound pressure ratio (75 Hz / 50 Hz) measured by the energization determination device of the AC electric arc furnace using an embodiment of the present invention with the difference in the slag-making state.

[0026] Figure 2 It is a graph showing the relationship between the high-frequency detection time rate determined by the device of the above embodiment and the electric power consumption rate index. Detailed Embodiment

[0027] Hereinafter, embodiments of the present invention will be specifically described. The following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and the structure is not limited to the following structure. That is, various changes can be made to the technical concept of the present invention within the technical scope described in the claims.

[0028] The energization state determination device of the AC electric arc furnace in the present embodiment (hereinafter referred to as "this device") includes a sound collection microphone as a detection unit for detecting the sound generated inside the arc furnace. In addition, this device includes an output unit that analyzes the frequency of the detected sound and outputs a frequency-intensity signal. This function can be implemented by hardware such as a computer or software. The microphone can be placed anywhere as long as it can hear the sound inside the electric furnace. It does not need to be placed near the electric furnace that becomes high temperature. In addition, this device includes a determination unit. This function can also be implemented by hardware such as a computer or software.

[0029] First, measure the sound of the frequency caused by alternating current power. The intensity of the sound pressure of a specified frequency can be directly measured, or the Fourier transform can be performed after measuring the sound pressure variation to compare the sound pressures of each frequency. It is also possible to compare the intensity ratio of the sound pressure signals of two different frequencies within a specified frequency range sandwiching the fundamental frequency. However, since the fundamental frequency itself sometimes varies slightly depending on the electrical system on the supply side, it is preferable to select at intervals of 10 Hz or more. Usually, there is a lot of interference such as ambient sound in the sound at frequencies far from the fundamental frequency. Therefore, when setting the frequency that is an integer multiple of the fundamental frequency F0 as Fi, it is preferable to use the signal intensity within the range of Fi - 0.5×F0 to Fi + 0.5×F0. In addition, it is preferable to set the difference between the two frequencies to 40 Hz or less. Therefore, the difference is preferably 10 Hz or more and 40 Hz or less.

[0030] The following is a detailed description.

[0031] Before the invention, the inventors confirmed that the sound generated from the alternating current arc is shielded by the foaming slag, resulting in a lower sound. It is known that a liquid containing bubbles significantly reduces the transmittance of high-frequency sound. Due to this effect, when the slag is in a foaming state, if the sound frequency is measured outside the furnace, the center frequency decreases. This frequency decrease is about several Hz, and although it can be perceived by listening carefully, it cannot be judged in the case of continuous change. Therefore, it is considered that the slag-making state can be stably detected by mechanical measurement.

[0032] The inventors carried out the energized melting of waste materials, etc. in an alternating current arc furnace with a tapping volume of 150 t scale and evaluated the effects. The electric furnace used in this embodiment is equipped with a water-cooled oxygen lance and a carbon injection lance, and can blow oxygen and carbon materials into the furnace respectively.

[0033] The operation mode is carried out in the following steps. First, load the iron source and auxiliary raw materials into the furnace. In the electric furnace used in this embodiment, about 80 t of molten steel is left for the next charging operation, and the iron source and auxiliary raw materials are loaded into this molten steel. Examples of the iron source include waste materials, pig iron, reduced iron, etc. In addition, examples of the auxiliary raw materials include carbonaceous materials, MgO sources for protecting refractories, lime for adjusting the slag composition, etc. After loading the raw materials or during the feeding process, power is supplied, and oxygen and carbon are blown in. Then, the iron source is sequentially added. When the amount of molten steel in the furnace reaches approximately 230 t, the temperature of the molten steel is adjusted to about 1600 °C, and tapping is carried out. The tapping volume is targeted at 150 t, and about 80 t remains in the furnace and is transferred to the next charging again.

[0034] A microphone for sound collection is installed in the same building as the above electric furnace. The microphone is installed at a distance of about 10 m from the electric furnace. Fourier transform is performed on the sound data measured by the microphone using an FTT analyzer, and the sound pressure is decomposed into each frequency. The frequency width at this time is set to 25 Hz, and the value obtained by dividing the sound pressure value of 75 Hz by the sound pressure value of 50 Hz is used as the sound pressure ratio (75 Hz / 50 Hz), which is output to the monitor in the electric furnace operation room. This sound pressure ratio (75 Hz / 50 Hz) is used as the energization pitch index. Representative results of the measurement are shown in Figure 1 . At this time, a camera for observing the inside of the furnace while charging from the furnace wall is used, and the observation is continued until the viewing angle is blocked by dust and slag. The fundamental frequency of the electric furnace used in this embodiment is 50 Hz. During operation, when the foaming state is maintained and the arc cannot be seen ( Figure 1 solid line), this energization pitch index varies between 0.4 and 1.0. However, when energizing in an unstable foaming state and the arc light is confirmed by the camera ( Figure 1 dashed line), the energization pitch index varies between 0.5 and 3.0.

[0035] [Example]

[0036] Using the same AC arc furnace as in the above embodiment, while monitoring the energization sound pitch index, the oxygen supply rate, the carbon material injection rate, and the slag-making material addition rate are adjusted on the basis of repeated tests so that the energization sound pitch index does not exceed 1.0. Lime is used as the slag-making material. The ratio of the time when the energization sound pitch index exceeds 1.0 to the energization time during operation is used as the high-pitch detection time rate, and the relationship between the power consumption rate index and the high-pitch detection time rate is shown in Figure 2 . The power consumption rate index is normalized with the maximum power consumption rate being 1.0. From Figure 2 , it can be seen that as the high-pitch detection time rate becomes shorter, the power consumption rate decreases. When the energization sound pitch index (sound pressure ratio (75 Hz / 50 Hz)) can be kept below 1.0 for most of the period, the power consumption rate index is about 0.8. By operating while monitoring the energization sound pitch index in this way, the energization efficiency is improved and the power consumption rate is reduced. This is because the slag-making state is maintained during energization, and the radiant heat from the arc can be shielded by the slag.

[0037] In this specification, [t] as a mass unit represents 10 3 kg.

[0038] [Industrial Applicability]

[0039] The hot metal produced by the AC electric arc furnace and its operation method of the present invention is useful as a method for obtaining high-purity hot metal because nitrogen absorption becomes difficult. In addition, according to the AC electric arc furnace and its operation method of the present invention, the accidental arc energization of the furnace wall composed of refractory materials and water-cooled plates is reduced, which also helps to improve the furnace life.

Claims

1. An apparatus for determining the energized state of an alternating current electric arc furnace, comprising: A detection unit that detects the sound generated inside the alternating current electric arc furnace; An output unit that analyzes the frequency of the detected sound and outputs a frequency-sound pressure signal; and A determination unit that, when setting the frequency that is an integer multiple of the fundamental frequency F0 of the alternating current electric arc furnace as Fi, determines the coverage state of the arc caused by slag formation based on the signal intensity within the range of Fi - 0.5×F0 to Fi + 0.5×F0.

2. The apparatus for determining the energized state of an alternating current electric arc furnace according to claim 1, wherein When setting the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination unit makes a determination based on the signal intensity of the center frequency within the range of Fi - 0.5×F0 to Fi + 0.5×F0.

3. The apparatus for determining the energized state of an alternating current electric arc furnace according to claim 1, wherein When setting the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination unit makes a determination based on the intensity ratio of the signal intensity of one of the higher frequencies and the signal intensity of one of the lower frequencies within the range of Fi - 0.5×F0 to Fi + 0.5×F0.

4. The apparatus for determining the energized state of an alternating current electric arc furnace according to claim 3, wherein The difference between the two frequencies for obtaining the intensity ratio is 10 Hz or more and 40 Hz or less.

5. An operation method of an alternating current electric arc furnace, when melting and refining scrap to produce molten steel in an alternating current electric arc furnace, Based on the energized state determined by using the apparatus according to any one of claims 1 to 4, control is performed on any one of the supply rate of oxygen-containing gas, the supply amount of carbon material, and the input amount of slag-forming material, or control is performed on a combination of multiple ones of them.

6. An alternating current electric arc furnace, comprising the apparatus according to any one of claims 1 to 4.

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